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 Subject: Bee hitting Train Category: Science > Physics Asked by: thegerbil-ga List Price: \$5.00 Posted: 04 Apr 2006 14:47 PDT Expires: 04 May 2006 14:47 PDT Question ID: 715458
 ```A bee is traveling at 5 MPH, and a train travelling in the opposite direction at 100 MPH. The Bee collides with the train, now travelling at the same speed as the train. Does the Bee at any point hit 0 MPH?```
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 Subject: Re: Bee hitting Train From: pafalafa-ga on 04 Apr 2006 14:52 PDT
 ```I suppose, on average, the answer is yes. But what is happening in actuality is that the bee is disintergrating, and different parts of its hapless body are moving at different speeds, and even in totally different directions...the part of the bee in first contact with the train has reversed direction while (for the briefest instant) the rear of the bee is still moving forward.```
 Subject: Re: Bee hitting Train From: myoarin-ga on 04 Apr 2006 15:11 PDT
 ```Very vivid ... Can any object reverse direction without for an instant having zero motion?```
 Subject: Re: Bee hitting Train From: marcusl-ga on 04 Apr 2006 16:08 PDT
 ```"Can any object reverse direction without for an instant having zero motion?" No. PS do your own homework gerbil, or you'll never be the one answering the questions.```
 Subject: Re: Bee hitting Train From: markvmd-ga on 04 Apr 2006 19:40 PDT
 ```Paf is quite correct. If you watch automobile crash video in slow motion, you can see that areas of the car that has hit a stationary object are still moving at quite a clip. In a 60 mph crash, the front of the car is effectively motionless rather quickly while the back of the car continues forward at ever reducing speed. Same with the poor bee.```
 Subject: Re: Bee hitting Train From: kottekoe-ga on 04 Apr 2006 20:21 PDT
 ```If we assume that the velocity of any part of the bee (or the average of all its parts) is a continuous function, then by the intermediate value theorem http://mathworld.wolfram.com/IntermediateValueTheorem.html it follow that the velocity must be zero at some point in time. If time or space is discreet, perhaps the velocity it is not continuous, but we have no useful theory of physics that predicts such a thing.```
 Subject: Re: Bee hitting Train From: probonopublico-ga on 04 Apr 2006 21:05 PDT
 ```I must point out that the moment the train hits the bee, the bee stops beeing. It then becomes a has-been. For members of the non-scientific community, it is clearly a case of seeing is beelieving.```
 Subject: Re: Bee hitting Train From: ronplz-ga on 05 Apr 2006 03:29 PDT
 ```Last thing to go through bee's mind after such an event? His back-side!```
 Subject: Re: Bee hitting Train From: myoarin-ga on 05 Apr 2006 03:46 PDT
 ```Or, as I once read, a frequent remark on "black box" voice recorders is: "Oh shit!"```
 Subject: Re: Bee hitting Train From: marcusl-ga on 05 Apr 2006 08:40 PDT
 ```yes yes gerbil, quote the intermediate value theorem as evidence, your 3rd grade prof will think you're brilliant =)```
 Subject: Re: Bee hitting Train From: kemlo-ga on 05 Apr 2006 10:19 PDT
 ```I've always thought a frequent remark on "black box" voice recorders is: Here, hold my beer, i'm going to try something different;)```
 Subject: Re: Bee hitting Train From: irlandes-ga on 05 Apr 2006 17:18 PDT
 ```Actually, and seriously, I suspect there is no guarantee that a bee can hit a train moving at 100 mph. The reason I say this is at that speed there is a large cushion of air in front of the train and it may well "blow" the bee aside rather than hit it. If of course depends upon the shape of the train's front, and the weight of the bee, and the exact point the bee approaches the train.```
 Subject: Re: Bee hitting Train From: ronplz-ga on 05 Apr 2006 23:30 PDT
 ```Tell that to all the bugs that commit harri-kirri on my car windscreen when I take a trip. The "cushion of air" may slow down the impact, but it certainly doesn't stop the inevitable splat! :-)```
 Subject: Re: Bee hitting Train From: mikewa-ga on 06 Apr 2006 09:59 PDT
 ```pafalafa has provided the real solution, but I saw this first as part of a paradox. ? for the bee to switch directions, it must stop at some point ? it seems reasonable that this occurs when it hits the train ? while the bee is on the train, they yare both moving at the same speed ? therefore: if the bee stopped, the train must have stopped also```
 Subject: Re: Bee hitting Train From: marcusl-ga on 07 Apr 2006 12:31 PDT
 `the train ain't reversing directions mike, the bee is. a paradox it is not.`
 Subject: Re: Bee hitting Train From: markvmd-ga on 07 Apr 2006 19:31 PDT
 ```I love thought experiments. The question can be phrased in a number of different ways. A stationary bee is hovering, gets plastered by the high-speed train; is the bee's speed ever below 100mph? Sure, that's one you can see. If it is below 100mph, you can assume it might be zero at some point. Instantaneous is a tough sell. Replace the bee with a rubber ball and you can visualize the elastic deformation and subsequent acceleration. Now toss the ball at the moving train. Still see the deformation and acceleration? Sure. Can the ball's speed ever be zero? Yep, but you can start to see that some parts may be moving while other parts are at zero speed. Isn't this covered under "velocity" in physics? Replace the rubber ball with a steel one and toss it at the train. A bit harder to visualize, but still possible. Watch out for transit cops. Now replace the train with a Hupmobile. Replace the ball with a turkey, which we used to call a "walking bird." Stand on your head. Put your right foot in. Put your right foot out. Hah, I didn't say "Simon Sez!" Man, it's been a long day.```
 Subject: Re: Bee hitting Train From: mikewa-ga on 10 Apr 2006 07:53 PDT
 ```marcusl i think you misread my comment: it was a tongue-in-cheek use of bad logic and never suggested the train reversed direction```
 Subject: Re: Bee hitting Train From: hackmonkey-ga on 11 Apr 2006 15:11 PDT
 ```"Does the Bee at any point hit 0 MPH?" NO The train is ALWAYS moving at 100mph...hitting the bee does not effect the train and therefore there will never be a point that the be is not moving through space......```
 Subject: Re: Bee hitting Train From: marcusl-ga on 27 Apr 2006 18:07 PDT
 ```mikewa ha, my bad. =) for you others, NO, the train is NOT always moving at 100mph. it slows down, albeit very slightly. momentum in the normal direction is conserved, mass of the bee * initial velocity of bee + mass of the train * initial velocity of the train = final mass bee *final velocity bee + final mass train+final velocity train.```
 Subject: Re: Bee hitting Train From: marcusl-ga on 27 Apr 2006 18:07 PDT
 `hackmonkey, you're totally incorrect. nothing can change directions instantaneously.`
 Subject: Re: Bee hitting Train From: probonopublico-ga on 27 Apr 2006 20:25 PDT
 ```marcusl-ga, QUOTE Nothing can change directions instantaneously. UNQUOTE You're totally incorrect! A woman's mind. (Haven't you seen them drive?) They call it 'multitasking'.```
 Subject: Re: Bee hitting Train From: aridley-ga on 03 May 2006 02:30 PDT
 ```Yes, for a very small time the bee stops, but the it is re-accelerated in the other direction, what is very interesting is that if the bee for an instant is doing 0 MPH the it follows that teh train for an instant must also be traveling at 0 MPH, but this does not happen because thh train slightely elasticly deforms, which allows the bee to hit 0 MPH and the re-accelerate it in teh other direction.```
 Subject: Re: Bee hitting Train From: myoarin-ga on 03 May 2006 07:16 PDT
 ```I disagree with the above, Newton's laws of motion, and so on. Going back to Pafalafa's comment, and forgetting for the moment that the bee will disintergrate, I believe that the center of mass of a less deformable object will stop for an instant, a small steel ball for example.```
 Subject: Re: Bee hitting Train From: mathisfun-ga on 06 May 2006 19:58 PDT
 ```Also if the bee is sliding along the front of the train for the instant it takes to change direction then it never was going 0 mph due to its movement along the front of the train, making kind of a parabolic path.```
 Subject: Re: Bee hitting Train From: cojones893-ga on 06 May 2006 21:35 PDT
 ```I might not bee the best to ask, but the second the bee hit the train wouldn't it already start beeing pushed in the opposite direction? Almost skipping zero?```